The present invention relates to a ventilation device having a fan wheel which includes a hub for securement of the fan wheel to a shaft. Furthermore, the present invention relates to an electric machine with such a ventilation device and to a respective manufacturing process.
Ventilation devices are normally used in high-powered electric motors in which the surrounding medium is no longer sufficient to provide a natural cooling. There is the option to actively ventilate the electric motors, i.e. provision of an additional fan motor with fan wheel for attachment to the electric motor to realize cooling of the electric motor. In addition, there is the option to cool an electric motor through self-ventilation by mounting a fan wheel to the shaft of the motor rigidly or via a coupling.
Electric motors for rail-bound and track-bound vehicles, such as three-phase rail traction motors, are increasingly operated at high rotation speeds in order to keep the motor torque and thus the motor weight as well as the size small. According to DE-B-25 14 265, the motor cooling is implemented by providing a fan wheel which is fixedly mounted to the motor shaft and which is driven by the respective motor speed and draws or pushes the ambient air either through the motor or through particular external cooling ducts. Such a fan wheel, fixedly mounted in this manner to the motor shaft, has the drawbacks that, on one hand, the amount of cooling air is always proportional to the motor speed, and, on the other hand, the fan wheel generates extremely annoying noises when rotating at high speeds.
To eliminate these drawbacks, the motor cooling according to EP 0 826 266 B1 provides for a fan wheel which is freely rotatably supported by the motor shaft. Disposed between the motor shaft and the fan wheel is an electromagnetic speed limiting and control unit which restricts the transport of cooling air in accordance with the required amount of cooling air. At a predetermined motor speed, the rotation speed of the fan wheel is reduced in relation to the motor speed by rendering the engagement action of the electromagnetic speed limiting device, configured as induction coupling, almost ineffective as the rotation speed of the motor shaft increases. As the motor speed drops, the engagement action is re-established until fully restored. Thus, the cooling air is made available at sufficient amount, when the motor speed is low, while the amount of cooling air to be transported no longer rises proportionately to the increase in motor speed, when the motor speeds are higher or high. Further, the energy consumption and the noise generation of the fan, in particular at high rotation speeds, is significantly reduced. The fan wheel used there, is so constructed as to have a short-circuit winding in the hub of the fan wheel. Manufacture of such an electromagnetic induction coupling is relatively complicated.
EP 1 024 295 A1 discloses the manufacture of the fan wheel or of the hub of the fan wheel from non-ferromagnetic material, e.g. aluminum. As aluminum is not ferromagnetic, the coupling effect between the fan wheel of aluminum and the motor shaft with permanent magnets is relatively slight. In addition, this printed publication describes the support of a fan wheel in a bearing plates or casing and the provision of an associated electromagnetic induction coupling.